Recently, as a virtual reality visual display system that can give presence--the same feeling as if placed in a real situation--an immersive projection display which encloses viewers with a large screen projected in from the back has drawn attention. A sphere is an ideal shape for an immersive screen in that a distance from the viewer's eye to the projected images remains constant.
As a solid angle subtended by an image with respect to a viewer becomes larger, it is impossible to project the image sufficiently. Therefore, conventionally, from a plurality of plane screens was formed a polyhedral screen, on which the images recorded by a plurality of wide angle cameras corresponding to the plane screens were thrown by projectors.
However, when a plurality of cameras arc used, there is a dead angle between adjacent cameras that does not allow recording. The dead angle may be negligible with respect to a subject in the distance, but as for a subject close by, the image of the subject corresponding to the distance between the edges of the lenses of adjacent cameras is missing.
The structure in a combination of plane screens produces a problem in that the ridges in the seams of each screen give an unnatural impression. In CG (Computer Graphic) images, a geometric correction is made to cope with the problem. Making a correction of recorded images, especially motion images, is difficult in original formatting stages. To do this, a plurality of cameras arc needed and it takes time to correct the original images, which increases cost.
To solve, in principle, the problems of the dead angle and seams, it is necessary to obtain the images of a large solid angle by a single-system camera and project them onto a spherical screen by a single-system projector. Conventionally, as a means of a single-system projector throwing images on a spherical screen, fisheye lenses were used to throw image onto a semi-spherical screen. Yet, since the means produces a shadow when a viewer enters a semi-sphere projection screen, a viewer must view the screen from the outside of the semi-sphere, indicating that, in principle, enclosing a viewer at a solid angle of more than 2.pi. is impossible. As a result, the means is not suitable to an immersive projection display.
In addition, a means can be thought of that, by a computer, controls, moves and tilts a reflecting mirror for the light from one projector to project in a wide range of angles onto a spherical screen. Yet that system cannot project entirely onto a spherical surface, and the structure is complex and expensive.
It is an object of the invention to solve the problems in the prior art. There is provided a full-surround spherical screen projection system that forms a spherical screen inside of a sphere, places a single-eyed projector, over a viewer, for projecting images in the inner direction of the sphere, provides, inside of the spherical screen, a first reflecting mirror opposed to the projector, provides a second reflecting mirror adjacent to the projector, and projects the images through the first and second reflecting mirrors from the projector on the screen. The screen projection system can throw images on the entire surface of the spherical screen except for the top and bottom of the sphere, with a wide visual field angle to the upper and lower directions and without casting a shadow by the viewer. The screen projection system is simple in structure, low in cost and spacious for the viewer.
The full-surround spherical screen projection system can be used to throw recorded images and CG images. At the stage of making original images to be thrown, distortion may be added to the original images beforehand. When thrown onto the spherical screen, the distortion of the images will be cancelled out to produce images without distortion.